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Biraj Biraj
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Posts: 434
A month ago
Consider a solution containing liquids A and B where the mole fraction of B is 0.60. Assuming ideality, calculate the mole fraction of A in the vapor at equilibrium with this solution at 25°C. (The vapor pressures of pure liquid A and B at 25°C are 117.7 torr and 400.0 torr, respectively.)
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CathygoldieCathygoldie
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A month ago
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Dalton's Law is different from what you wrote. For a 2-component solution:

P_soln = P1p*X1 + P2p*X2

here P_solution is the vapor pressure of the solution
P1p is the vapor pressure of pure component 1
P2p is the vapor pressure of pure component 2
X1 is the mole fraction of component 1 in solution
X2 is the mole fraction of component 2 in solution.

The individual vapor pressures of components 1 and 2 are given by:

P1 = P1p*X1
P2 = P2p*X2

Now calculate the total pressure as follows:


X1v = (P1p*X1)/P_soln = P1p*X1/(P1p*X1 + P2p*X2)
X2v = 1-X1v = P2p*X2/(P1p*X1 + P2p*X2)

Plugging in the values you were given:

P_soln = 0.4*117.7 torr + 0.6*400 torr

= 47.08+240

= 287.08 torr

X1v = (117.7 torr * .4)/(287.08 torr) = 0.164

X2v = 1-X1v = 0.836
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